The present invention relates to a method of starting a gas turbine and, in particular, to a method in which an abrupt change in temperature of combustion gas at the time of starting the turbine is suppressed to reduce thermal stress and surface oxidation of component parts forming a path for the combustion gas so as to prolong the life of the component parts.
A method of starting a gas turbine has hitherto been generally employed to accelerate the turbine in such sequence that the turbine is warmed up using a cranking motor, a combustor is ignited at a certain flow rate of fuel injected thereinto, and the fuel flow rate is gradually increased.
At the time of ignition, since a fuel air ratio at that time is large, a gas temperature at the inlet of the turbine varies sharply, which causes the metal temperature of turbine structural members to sharply change.
Further, in general, stationary blades and moving blades are cooled with cooling medium introduced inside the blades, and the blades each have a large temperature difference between a leading edge and a trailing edge thereof and between an inside surface and outside surface thereof, so that thermal stresses are caused in most parts of each blade. Further, the temperature difference to lapse time becomes larger in the middle of turbine acceleration. Oxidation on surfaces of components forming a path for combustion gas is likely to be caused. The above-mentioned large thermal stresses and the surface oxidation reduce the life of the turbine.
A conventional method of warming up a gas turbine, wherein an exhaust gas temperature at the time of warming up is taken in as a control element and a fuel flow rate is controlled so that a gradient of the temperature will be within an allowed range thereof, is disclosed in Japanese Patent Laid-Open No. 55-114855/1980.
According to conventional method, the time period until the turbine reaches a rated rotational speed, that is, the starting time is prolonged.